The present generation of human kinds is fascinated towards small and beautiful microelectronic devices. In this regard, future microelectronic industries require tiny device area with more and more data bits i.e. large logic bits density with low power consumption and less heat dissipation. Our microelectronic devices and their technology node have reached a threshold condition where classical physics assumptions, boundary conditions, and related physics have failed to explain the unusual physical and functional properties due to tunneling effect and wave-particle duality. Memory industry physicists and technocrats are also facing another major challenge to control the excessive heat dissipation and large leakage current with lowering the physical thickness of devices to increase more and more bit densities. Moore's Law predicts the doubling of integrated circuit after each two years, which is valid till now, however the fast progress in the data storage technologies cannot meet the requirements just by the miniaturizing of devices. At present we need something more than Moore's law in terms of the materials as well design. Ferroelectric memory industries are also facing the similar problems; the potential materials show poor charge retention and large leakage with reduction of size. Therefore, it is imperative to develop novel ferroelectric materials and phenomenon for high component density memory devices with low power consumption. In this context, optically control of polarization is highly expected to help the industry to a regime beyond the Moore's law.
Prof J. F. Scott, University of Cambridge, UK, which is also known as father of ferroelectric memory, has developed and proposed several ferroelectric materials and processes to develop commercial ferroelectric random access memory (FeRAM), (J. F. Scott, Ferroelectric memories, Springer-Verlag, (2000)).
U.S. Pat. Nos. 6,778,422 and 7,050,323 propose a nonvolatile memory cell in the form of static random access memory, which was composed of ferroelectric capacitors and transistors for amplification and allows high speed write and read applications. It emphasized basically the electric circuits; cell array and its connections with ferroelectric capacitors for high speed output write and read process. The embedded ferroelectric capacitors comprise of very common lead zirconate titanate (PZT) ferroelectric materials, based on electrically high speed write and read process of ferroelectric capacitors and transistors for amplification in contrast with present approach of optically read process for multi logic states.
U.S. Pat. No. 7,205,256 B2 proposes the fabrication of several perovskite ferroelectric thin films utilizing the modified solution-deposition technique, preparation of gel-solution for forming the perovskite or lamellar perovskite structure oxide formed by mixing of alkoxides or organic acidic salts of two or more kind of metals required for the desired ferroelectric materials.
European patent No: EP 1411031 A1/WO 2002/102712 deals with a process for manufacturing the ferroelectric ceramics/films having oxygen octahedral with layered structure and paraelectric materials for catalyst.
US patent No: US 20130037092A1 claims the diode like characteristic of ferroelectric BiFeO3 (BFO) thin films sandwiched between semitransparent electrodes. US patent No: Pub. No.: US 20110308580 A1 describes the ferroic BiFeO3 material for nano-electronics, logic circuits, and memory device applications. This invention describes the intrinsic conducting domain walls separated by insulating walls and therein the formation of controlled network of 2 nm conducing walls on the 2D insulating sheet. It also provides the methods of writing, reading, erasing, and manipulating the conducting walls for memory applications. According to various embodiments, optoelectronics and photovoltaic devices are described. The major drawbacks of these patents are as follows: (i) it deals with highly conducting BiFeO3 thin films contrast to our novel materials, (ii) major focus on the switching behavior of photocurrent and diode characteristics, and (iii) do not illustrate with the switching of ferroelectric polarization or displacement currents.
References may be made to Nature Communications|4:1990|DOI: 10.1038/ncomms2990, (2013) wherein Guo et al., reported the Non-volatile memory based on the ferroelectric photovoltaic effect. Another recent discovery on development of perovskite oxides for visible-light-absorbing ferroelectric and photovoltaic materials are described by Ilya Grinberg et al., in Nature, 503, 509 (2013); doi:10.1038/nature12622.
Generally classical ferroelectrics are well known that any kind of leakage current is detrimental for polarization switching based nonvolatile memory elements. However it has been established that rectification direction and the direction of photovoltaic current are closely related to the direction of electric polarization of ferroelectric photovoltaic. In this regard, our present invention can be utilized for potentially low energy, high density, low power, and less heat dissipation nonvolatile multi states memory elements, photodetectors, interface mediated photovoltaic to tunnel the photocurrent with above bandgap open circuit voltage, and also domain walls based photo energy harvesters.
Another reference made to Nature materials, 11, 260, (2012) wherein J. Kreisel, M. Alexe and P. A. Thomas explained the importance of photoferroelectric material and emphasized that it is more than the sum of its parts. Above mentioned reports basically demonstrate the photovoltaic aspect of the ferroelectric photovoltaic, wherein our present invention deals with novel single phase ferroelectric material with significant photocurrent and optically switchable polarization.
Most of the prior art deals with the electrically write and read process of ferroelectric polarization for nonvolatile memories require high power consumption and large area device miniaturization.
The present invention is about the optically active classes of ferroelectric materials where optical control of polarization is expected to play a pivotal role in memory devices to meet with the current demands. The present invention deals with the electrically write and optically read process which may provide nanoelectronic devices with low power consumption, less heat dissipation, and tiny device area. Among all the prior arts, BiFeO3 has shown ferroelectric photovoltaic property due to inbuilt polarization; however present invention also shows another family of perovskite with high ON/OFF switching current, open circuit voltage, and short circuit current. Our invention allows much faster approach for read and write operation ferroelectric capacitors and transistors which deal with optical monochromatic laser light and white light. Another aspect of this invention is to provide a plurality of the above diodes in an electronic memory device. It also provides a photovoltaic device of single crystalline polar ferroelectric sandwiched between two semi-crystalline electrodes. Another aspect of this invention includes the solar cell based on the polarization of ferroelectric; these cells may either connected in series or parallel.